Multi-Objective Design of a Biodegradable Coronary Artery Stent - Cardiovascular and Cardiac Therapeutic Devices - page 7

Fig. 3 Generic polymer scaffold with out-of-phase rings (based on the ART18AZ platform)

Thus, there are four polymeric devices with in-phase rings and three with out-
of-phase rings. The four in-phase devices are topologically very similar, although
the Ideal BioStent differs due to having very wide struts.
The three out-of-phase devices have more significant differences with respect to
the arrangements of bridges between adjacent rings. In particular, the ART18AZ
design has alternating pairs of rings that form arrays of closed and open cells (c.f.
Fig. 3 ).
The Acute device (Orbus-Neich) is less obviously defined in the same way as
the seven above. However, in its expanded shape, it can be described as com-
prising arrays of closed cells (formed by pairs of adjacent rings) with each array
joined by three inclined, longitudinal bridges. Since the lengths of the bridges are
comparable to the longitudinal length of each closed cell array, it can be classified
as a hybrid device.
The two remaining well known biodegradable scaffolds have significant char-
acteristics that distinguish them from the other eight. The ReZolve2 device (Reva
Medical) is polymer based and balloon expandable, but it has a unique slide and
lock mechanism. The DREAMS2 device (Biotronik) is the only non-polymeric
bioresorbable scaffold; made from magnesium alloy, it looks like a conventional
metallic stent. Geometrically, it can be classified as an open cell device with wavy,
in-phase rings joined by wavy mid-strut links.
Most of the information described above has been obtained directly from
company internet pages and complemented by images and details in the literature
[ 13 , 19 ]. Accurate dimensions have not been obtained for all platforms and, in
general, only strut thicknesses are publicly available. Based on the available data,
all known thicknesses range between 150 and 200 lm for polymeric devices, but
the magnesium alloy DREAMS device is 125 lm thick. As discussed above, these
thicknesses are significantly larger than those for state-of-the-art permanent
metallic stents. This suggests that current and future research is likely to focus on
reducing the thickness (and the width) of bioresorbable scaffolds. Essentially,